Honda S2000 (AP1/AP2) Rear Differential Fluid Change
- Never work under a car held only by a jack; use four jack stands on solid ground.
- Do not remove the drain plug until the fill plug is out.
- Gear oil has a strong sulphur smell and irritates skin; wear gloves.
Introduction
Changing the S2000's rear differential oil is one of the quickest fluid jobs on the car, and a single quart bottle is enough. Two things matter. First, have the car level so the old oil drains fully and the fill hole shows the correct level. Second, remove the fill plug before the drain plug, so you can never end up with an empty differential that you cannot refill. Both plugs get new sealing washers and are tightened to 33 lb-ft, which is the figure in the writeup and the figure an S2KI member quoted from the 2000-2005 service manual. Adapted from a community writeup by SIIK2NR on S2KI (https://www.s2ki.com/s2000/topic/348700-differential-fluid-change/).
Procedure
10 steps-
Step 1: Raise the car level on four stands
Chock the wheels, jack the car and set it on four jack stands so it sits level front to rear and side to side. A level car lets the old oil drain completely and makes the fill hole a true level check. Push firmly on the car before you go underneath to make sure it is stable on the stands.
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Step 2: Find the two plugs
From under the rear of the car, find the differential. The fill plug is higher up on the housing and the 24mm drain plug is at the bottom. There is very little clearance around the fill plug, so S2KI members usually use an ordinary wrench on it instead of a socket.
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Step 3: Soak the plugs
Spray both plugs with penetrating oil and give it a few minutes. These plugs are often very tight from the factory or the last service.
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Step 4: Remove the fill plug first
Break the fill plug loose with the 23mm wrench and remove it, keeping track of its washer. Always do this before touching the drain plug: if the fill plug will not come out, you can stop with the diff still full instead of being stranded with an empty one.
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Step 5: Drain the old oil
Set the drain pan under the diff, break the 24mm drain plug loose with the breaker bar and remove it. The oil runs straight down and takes a few minutes to empty.
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Step 6: Clean the plugs and fit new washers
The drain plug is magnetic. Wipe it clean and look at what it collected: a fine grey paste is normal, but chunks or flakes are not. Clean both plugs and fit the new washers, 90401-PCZ-003 on the drain plug and 90402-PCZ-003 on the fill plug.
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Step 7: Reinstall the drain plug
Once the dripping has stopped, start the drain plug by hand so it cannot cross-thread, then torque it to 33 lb-ft.
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Step 8: Pump in new oil
Fit the hand pump to the bottle, put its hose into the fill hole and pump. Stop when oil starts to run back out of the fill hole. That overflow point is the correct level.
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Step 9: Reinstall the fill plug
Once the excess has stopped dripping, thread the fill plug in by hand and torque it to 33 lb-ft. If your torque wrench will not fit between the differential and the crossmember, one S2KI member tightens it with a plain wrench to about the same feel as the drain plug and checks it for seepage afterwards.
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Step 10: Clean up and check
Wipe the housing clean so any future seep is easy to spot, lower the car, and check both plugs for drips after the first drive. Take the old oil to a recycling point.
- Buy the two washers from a Honda parts counter ahead of time; they are inexpensive and the crush washers should not be reused.
Related procedures
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